Early detection of breast cancer and other types of cancer is typically an important factor in successful treatment. Ultrasound tomography is a promising imaging modality that has the potential to improve medical imaging of tissue for screening and diagnosis purposes compared to conventional imaging techniques. For instance, mammography is the current standard for breast screening, but involves ionizing radiation that precludes frequent imaging, and mammography has low sensitivity for detection of cancer in patients with dense breast tissue, which leads to a relatively high false negative rate. As another example, magnetic resonance imaging (MRI) is prohibitively expensive for routine use and also has limited accessibility.
A basic principle of conventional ultrasound involves emitting an acoustic wave or beam along a focused path from a source transmitter, and allowing the wave to scatter (e.g., in reflection, refraction, diffraction, transmission) from tissue or other boundaries in its path. The scattered wave returns to a surface of one or more receiving elements, which can be centered around and/or include the transmitter(s). The time of travel can be converted into a depth distance by multiplying the time by an assumed speed of sound in the media. The received signal is then output to a graphical display for user interpretation. Image reconstruction methods used by current ultrasound systems are, however, limited by the wavelength of ultrasound used, and typically fail when the characteristic dimension of a lesion is similar in dimension or smaller than the wavelength of ultrasound used. Additionally, current ultrasound systems and methods are typically configured to accommodate a small imaging region, resulting in difficulties in imaging and characterizing entire organs, such as the breast. As an additional factor, measurement of tissue parameters and provision of analyses derived from such measurement are limited in current systems due to deficiencies in current ultrasound systems and methods for generating and processing signals. Furthermore, the performance of ultrasound scanning is dependent on the skills of the operator and image quality can vary from user to user.
Thus, there is a need in the ultrasound imaging field to create an improved ultrasound waveform tomography method and system. This invention provides such an improved method and system.